1. Field of the Invention
The present invention relates to an apparatus for and a method of reclaiming molding sand, and more particularly to an apparatus for and a method of reclaiming molding sand capable of increasing a recycling efficiency of used molding sand and of highly enhancing the purity of a reclaimed molding sand, which is capable of prevent the reclaimed molding sand from being damaged and of simplifying the total construction of the apparatus for reclaiming molding sand relative to the conventional molding sand recycling apparatus, by removing coking agents sticking on a surface of the used molding sand due to a collision and a mutual frictional rolling contact between the used molding sand and a rotatable grinding drum during rotation of an impeller in a casing after having accomplished charging the used molding sand toward the impeller in the casing, and thereafter by exhausting fine powders of coking agents, which are segregated from the used molding sand, through a dust collecting port together with external air introduced into the casing through an inlet pipe of a rotational shaft.
2. Description of the Prior Art
Casting process, which has been widely used for manufacturing a metal product, includes several steps of forming a molten metal by heating a metal at its melting point, pouring the molten metal into a molding box having a shape that is exactly the same as a desired metal product, cooling and solidifying the molten metal in the molding box.
In the conventional casting process as described above, the molding box used for molding a molten metal into a product is formed by using a molding sand composition, which comprises silica sand having an excellent refractoriness as main component. This molding sand composition combines sand having about 20 to 70 mesh size, about 4 to 8% of clay as a coking agent, and about 2 to 6% of moisture. The molding box is produced by pouring the molding sand composition as described above into a mold, in which a desired pattern is provided therein, and by continuously solidifying it therein.
However, when a cast-iron product is produced from the conventional molding box, the coking agent is sticking on the surface of molding sand due to high temperature of the molten metal. If this used molding sand having the coking agent sticking on the surface thereof is used for next casting of a product without performing any additional process for removing the coking agent, then a mutual combining force between molding sands is weaken and the ventilation between molding sands deteriorates, which always leads to a harm to a cast-iron product. In order to solve these problems, it always needs to remove the coking agent sticking on the surface of the used molding sand and continuously revive new molding sand having a desired purity.
There are many techniques and procedures well known in the art by which used molding sand is recycled. For example, the first type of recycling technique is that used molding sand is sprayed toward a grinding piece at a high speed. This recycling technique provides an excellent processing performance. However, a problem associated with this processing used molding sand into reclaimed molding sand is that the grinding piece is severely partially worn away, which always needs a frequently replacement of the grinding piece, and leads to an increased cost of reclaiming used molding sand. Other problems associated with this recycling technique are that molding sand may be easily brown down owing to a strong collusion against the grinding piece and it is very hard to separate fine powders of coking agents and fine powders of the grinding piece from reclaimed molding sand.
Alternatively, the second type of recycling technique is that used molding sand is processed by mechanically vibrating it in a vibrating device with the aid of air stream. However, one problem associated with this processing used molding sand into reclaimed molding sand is that the total construction of the vibrating device used for performing this technique is very complicated, which always needs much time and brings about an increase in cost of producing recycled molding sand having a desired purity.
Alternatively, the third type of recycling technique is that used molding sand is washed by water. However, one problem associated with this processing used molding sand into reclaimed molding sand is that it is very hard to remove the coking agent sticking on the surface of used molding sand by using only this washing technique, which always needs for installing additional devices such as a vibrating device and brings about an increase in cost of producing a reclaimed molding sand.
In the mean time, when a resin is used as a coking agent for molding sand, the resin is removed from a surface of the molding sand by heating used molding sand at a high temperature. However, in order to heat the used molding sand at a high temperature, it is necessary for installing additional heating devices and brings about an increase in cost of producing a reclaimed molding sand.
The fourth type of recycling technique is that used molding sand is processed by charging it in a rotatable grinding drum, continuously rotating the grinding drum and inducing a mutual frictional rolling contact between used molding sand and the grinding drum. It would be desirable to recycle used molding sand by using this recycling technique.
Conventional apparatus for reclaiming used molding sand having a rotatable grinding drum are disclosed in Korean Patent Publication No. 1981-1841 (Date of Registration: Nov. 17, 1981), Korean Laid-Open Patent Publication No. 1983-7177 (Date of Publication: Oct. 14, 1983) and Korean Laid-Open Utility Model Publication No. 1988-21514 (Date of Publication: Dec. 24, 1988), etc.
However, in these apparatus, coking agents sticking on the surface of the used molding sand may be removed by using a mutual frictional force generated between the grinding drum and the used molding sand during rotation of the grinding drum at a high rotation speed, which leads to special problems. One of the problems is that the operational efficiency relative to removing the coking agents deteriorates, which always needs a lot of time for completely removing the coking gents relative to the second type of recycling technique. Due to this reason, it has not been possible or practical to recycle the used molding sand as reclaimed molding sand having a high purity by only once performing the process of reclaiming used molding sand using the grinding drum.
Other problem associated with these conventional apparatus is that it is very hard to exhaust fine powders segregated from the coking agent through a dust collecting port, which always needs for installing additional devices such as an impeller for easily exhausting the fine powders and brings about an increase in cost of producing a reclaimed molding sand.
Another problem associated with these conventional apparatus is that the total constitution of the apparatus for reclaiming used molding sand becomes complicated and the total volume of the apparatus is very large. In other words, the conventional apparatus are provided with a sand distribution structure for uniformly charging used molding sand into the rotatable drum, a structure for reclaiming the used molding sand into reclaimed molding sand by using the rotatable grinding drum, a structure for exhausting reclaimed molding sand, and a blowing device for supplying external air into the casing, which always needs for spending a large amount of money and a lot of time in order to maintain and repair the apparatus for reclaiming used molding sand, and brings about an increase in cost of manufacturing the apparatus as described above.
The present invention is contrived to solve the foregoing problems. It is a first object of the present invention to provide an apparatus for reclaiming molding sand capable of increasing a recycling efficiency of used molding sand and of highly enhancing the purity of a reclaimed molding sand, which is capable of prevent the reclaimed molding sand from being damaged and of simplifying the total construction of the apparatus for reclaiming molding sand relative to the conventional molding sand recycling apparatus.
Also, it is a second object of the present invention to provide a method of reclaiming molding sand capable of increasing a recycling efficiency of used molding sand and of highly enhancing the purity of a reclaimed molding sand.
In order to achieve the first object, the present invention provides an apparatus for reclaiming molding sand having a casing constituted of a disc-shaped upper frame, a cylindrical middle frame and a disc-shaped lower frame, which are integrally formed together, in which a hopper for throwing used molding sand in the casing is installed at the upper frame of the casing, a dust collecting port for collecting and exhausting fine powers of coking agents segregated from used molding sand is installed at the upper frame, a reclaimed molding sand extrusion port for extruding reclaimed molding sand from the casing is installed at the lower frame of the casing, a rotational shaft is disposed in operative association with a motor at the center of the casing with vertically passing through the upper frame and the lower frame, characterized in that:
an impeller including pluralities of blades is disposed on the rotational shaft, the blades being formed at an outer peripheral surface of the rotational shaft and extending radially outwards at a predetermined length, in which an upper disc and a lower disc are formed at an upper end and a lower end of the blade, respectively, a tuyere is formed through the center portion of the impeller between the blades of the impeller and is fluid-communicated with an inlet pipe extending from the outside of the casing into the casing along the rotational shaft, a cylindrical grinding drum made of a grinding stone is disposed between the impeller and the middle frame of the casing, the grinding drum being spaced from radial free ends of the upper discs and the lower discs and being spaced from the middle frame at a predetermined distance.
Also, in order to achieve the second object, the present invention provides a method of reclaiming molding sand, of the type wherein a used molding sand is formed by crushing a lump of molding sand segregated from a molding box and is consequently reclaimed by removing coking agents sticking on a surface of the used molding sand, the improvement comprising:
rotating an impeller disposed in a rotatable grinding drum made of a cylindrical grinding stone, the impeller being spaced from the rotatable grinding drum at a predetermined distance;
removing the coking agents from the surface of the used molding sand due to collision and a mutual frictional rolling contact between the used molding sand and the rotatable grinding drum with the aid of rotational force of the impeller after having accomplished charging the used molding sand toward the impeller; and
exhausting fine powders of the coking agents, which are segregated from the used molding sand, through a dust collecting port together with external air introduced into the casing through an inlet pipe of a rotational shaft disposed in operative association with a motor at the center of the casing.
As described above, in the apparatus for and the method of reclaiming molding sand according to the preferred embodiment of the present invention, it is possible to process used molding sand into reclaimed molding sand with only once performing the sand reclaiming process. Furthermore, it is possible to prevent the rotatable grinding drum from being worn and to prevent the molding sand from being damaged relative to the conventional apparatus for and the conventional method of reclaiming molding sand using the molding sand recycling technique that the used molding sand is directly sprayed to a grinding piece with the aid of compressed air.